THE AMCEBA 



Phylum Protozoa Class Sarcodina 



Exercise 1. — Occurrence and General Activities. 



(a) Many species of the Genus Arnosba and its close relatives 

 occur in fresh water, others in moist soil, and some as parasites in the 

 digestive tracts of larger animals. The fresh-water amoebse are some- 

 times found abundantly in nature or in laboratory cultures, but such 

 cultures are difficult to maintain, and for this reason the amceba is not 

 so easily secured at specified times as are many other unicellular 

 forms. Very old hay infusions, prepared originally for paramecia, 

 may contain numerous amoebae. Ooze from the bottom of a pond 

 or stream, the floating scum, slime adhering to the stems and leaves 

 of water plants, and similar material sometimes contain great numbers. 

 In recent years special methods of laboratory culture have been de- 

 veloped. If you have opportunity, it is interesting to see the actual 

 collection in the field of material likely to contain this protozoan and 

 how the cultures are handled. In any case, examine the laboratory 

 cultures that contain amoebae, noting the general appearance, color, 

 and odor. 



(b) Secure a drop of material from a culture known to contain 

 amcebse; add small bits of a No. 1 cover glass so that the No. 2 cover 

 glass placed on the drop will not crush the specimens. Before return- 

 ing to your place in the laboratory, examine a demonstration having 

 an amoeba in focus in order to know what to look for with your own 

 microscope. Use a small aperture in the iris diaphragm, and look with 

 the low-power objective for small pale blue or gray translucent objects 

 containing minute granules. When a specimen is located examine it 

 with the high-power objective. Open and close the iris diaphragm 

 and observe the result. Why is it necessary to use a small aperture 

 in searching for amoebae and similar organisms? Observe the granules 

 closely. Are they in motion? Does the animal change shape? Is 

 there any relation between the movement of the granules and the 

 changes in shape? Does the animal accomplish definite locomotion? 

 Make a series of four drawings showing the shapes assumed by a 

 single individual at intervals of one minute during this amoeboid 

 movement. Omit all internal structures, show outlines only, and put 



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